1. Subsurface Weathering:
* Fractures and Joints: Bedrock is often fractured and jointed, providing pathways for water to infiltrate and penetrate deeper. These fractures can be created by tectonic activity, stress, or even the cooling and contraction of igneous rocks. Water seeps into these cracks and crevices, carrying dissolved chemicals that can cause weathering.
* Root Wedging: Tree roots grow into cracks in the bedrock, exerting pressure and expanding them over time. This process can physically break apart the bedrock, creating space for further weathering.
* Chemical Weathering: Chemical reactions can occur within the bedrock itself, even without direct contact with the atmosphere. For example, groundwater can contain dissolved carbonic acid, which can react with calcium carbonate in limestone to form soluble bicarbonate. This process, called karst weathering, leads to the formation of caves and sinkholes.
* Frost Wedging: While not as common beneath the surface, in areas with freezing temperatures, water can seep into cracks and freeze. The expansion of ice can exert pressure on the bedrock, causing it to crack and break. This process is more likely to occur in areas with alternating freeze-thaw cycles, where the water has access to the bedrock.
2. Weathering from Below:
* Erosion: Erosion by wind, water, or glaciers can gradually remove overlying layers of soil and rock, exposing the bedrock to the elements. This process can lead to the formation of cliffs, canyons, and other features where weathering continues to act on the exposed bedrock.
* Thermal Expansion and Contraction: Bedrock can experience thermal expansion and contraction due to changes in temperature. These changes can create stresses within the rock, leading to the formation of fractures and cracks that make it more susceptible to weathering.
In summary:
While weathering is often associated with the surface, it can also occur beneath the bedrock through a variety of processes. These processes are driven by the infiltration of water, chemical reactions, and physical forces that can break down the rock over time.
